The present invention relates to a method for monitoring a pollutant conversion capacity of catalytically coated, oxidizing exhaust gas aftertreatment components in an exhaust gas system of an internal combustion engine according to the preamble of claim 1 as well as to an open-loop and or closed-loop control device, a computer program and a computer program product according to the preamble of the respective coordinate claims. A monitoring of this type is, for example, typical when a three-way catalytic converter is used and is therefore per se prior art.
Stricter laws in the area of a diagnosis of emission related components require within the scope of on-board diagnostic systems (OBD) the monitoring of all exhaust gas aftertreatment components for compliance with limit values, which for the most part are specified as a multiple of the emission limit values. Complex exhaust gas aftertreatment systems are used in order to meet the required exhaust gas emission levels. SCR catalytic converters (selective catalytic reduction) among other things are used for the conversion of nitrogen oxides. A certain ratio of NO to NO2 in the exhaust gas is necessary for the SCR catalytic converter to function optimally. The proportion of NO2 should be at 50% or more. The NO2 proportion in the untreated emissions of the internal combustion engine is significantly smaller as a rule. Typically said proportion is at about 10% there. The NO proportion is correspondingly at about 90% in said untreated emissions. In order to provide the suitable NO2 concentration, an oxidation catalytic converter is disposed in the exhaust gas aftertreatment system upstream of the SCR catalytic converter, or a particle filter which is correspondingly catalytically coated is provided in order to oxidize NO to NO2. An elevated NO2 also facilitates a regeneration of the particle filter by oxygen from NO2 molecules being used for the oxidation of carbon of the embedded soot particles. By reducing the particle loading in the particle filter, a lower flow resistance and a longer loading phase are achieved. Both have a positive effect on the engine emissions.
Because these factors are important for the compliance with emission limit values, there are requirements in the OBD legislation, which must be met, in addition to the properties of the components contributing to said compliance. For example, the monitoring of the coating of the oxidation catalytic converter is required. A lack of monitoring leads to a violation of the OBD legislation and carries with it initially a fine to be paid per vehicle. If the deficiency is not taken care of within a time period determined by the lawmaker, the registration of the vehicle in question is in danger of being revoked.
There is currently no prior art method which monitors catalytically coated exhaust gas components for their capacity to convert NO to NO2.
According to the prior art, conclusions can be drawn about a NO2/NO concentration upstream of the SCR catalytic converter from operating parameters, respectively effect models. In the German patent specification DE 10 2998 004 222 A1, a measurement of the NO2 concentration in the exhaust gas between an oxidizing emission control component and the SCR catalytic converter is initially defined when determining a reducing agent quantity. The reducing agent quantity is subsequently determined from operating parameters of the SCR catalytic converter as well as from the measurement for the NO2 concentration in the exhaust gas between the oxidizing emission control component and the SCR catalytic converter.
The German patent specification DE 101 59 849 A1 indicates a method for the aftertreatment of exhaust gas of internal combustion engines, in particular for the reduction of a nitrogen oxide proportion of the exhaust gases, the nitrogen oxide being reduced in the presence of oxygen and a reducing agent. In so doing, at least a part of the NO present in the exhaust gas is previously converted to NO2.